Esters of oxidized hydrocarbon carboxylic acids and processes for preparing the same



United States Patent ESTERS OF OXIDIZED HYDROCARBON CAR- BOXYLIC ACIDS AND PROCESSES FOR PRE- PARING THE SAME Edgar I. Crowley, Pittsburgh, Harry J. Elder, Tarentum, and Norman W. Franke, Penn Township, Allegheny County, Pa., assignors to Gulf Research and Development Company, Pittsburgh, Pa., in corporation of Delaware No Drawing. Application November 25, 1955, Serial No. 549,157

19 Claims. (Cl. 260-452) This invention relates to esters of oxidized hydrocarbon carboxylic acids and to processes for preparing the same. More particularly, the invention relates to substantially neutral alkyl esters and alkyl thioesters of a mixture of carboxylic acids obtained by nitric acid oxidation of long chain saturated aliphatic hydrocarbons, and to processes for preparing these substantially neutral esters.

Substantially pure dialkyl esters and dialkyl thioesters of various dibasic carboxylic acids, as well as relatively simple blends of such preformed esters have heretofore been proposed for use as lubricants under circumstances where good performance is required at extreme service temperatures. For example, such esters have found use in the lubrication of gas turbine aircraft engines where low volatility at high altitude and high service temperatures is important, and where low temperature fluidity is also important. Esters of the type indicated have also found use in the lubrication of instruments, firearms and automotive engines and equipment which are required to function at extremely low temperatures.

An important disadvantage residing in the use of relatively pure esters of the kind indicated, or in the use of simple blends of such relatively pure esters, is the relatively high cost of the pure or substantially pure esters. For example, in one cost comparison published in July, 1954, it was noted that the cost of commercial diester synthetic lubricants was from five dollars to ten dollars per gallon as compared with fifty-five cents to seventy-five cents per gallon for military aviation grade oils.

According to this invention there is provided at relatively low cost a novel class of synthetic diesters suitable for use as lubricants. Broadly stated, the novel synthetic esters of this invention are selected from the group consisting of substantially neutral alkyl esters and thioesters of a mixture of dicarboxylic acids obtained by partial oxidation of long chain saturated aliphatic hydrocarbons with an excess of nitric acid of at least 50 percent strength, at a temperature of about 50 to about 150 C. for about one-half to 45 hours, said alkyl substituents containing 4 to 25 carbon atoms. The invention also includes methods of preparing the indicated class of esters.

The synthetic ester compositions of this invention are characterized principally by the presence in the ester mixture of the mixed acyl residues of the acids contained in a complex acidic mixture obtained by nitric acid oxidation of long chain saturated aliphatic hydrocarbons. The desirable properties of the ultimate ester composition are believed to be chiefly due to a propitious distribution, in the mixed acids used to form the ester composition, of dibasic acids, normally of the type containing terminal carboxyl groups and 3 to 16 carbon atoms per molecule, which have been found to comprise the principal portion of the mixture, and/or to the presence of appreciable proportions of other products of the nitric acid oxidation 2,815,358 Patented Dec. 3, 1957 that have not yet been definitely identified and which are of such complexity as to defy exact analysis.

The synthetic ester compositions of this invention can be prepared in any suitable manner. According to a preferred procedure, an oxidized acids mixture obtained from the nitric acid oxidation of long chain saturated aliphatic hydrocarbons is esterified with the desired monohydric alcohol or its thioanalogue. The conditions of esterification are convention and form no part of this invention. For the sake of clarity it is noted that the estcrification reaction can be satisfactorily carried out by reacting the oxidized acids mixture with at least an equivalent amount and preferably an excess, for example, a 3 :1 equivalent ratio, of the desired monohydric alcohol, preferably in the presence of a small amount of a suitable catalyst, e. g., sulfuric acid, hydrogen chloride, p-toluene sulfonic acid, or the like, for a period of about 3 to about 10 hours, for example 5 hours. The time of the reaction normally decreases, within limits, with increased mol ratio of reactants and with increased temperature of reaction. Although esterification can proceed to some degree at temperatures as low as room temperature, elevated temperatures of the order of about 60 to 250 C. are preferably employed. When temperatures exceeding the boiling point of water are used, water of esterification can be trapped off, thus tending to drive the reaction to completion.

In modifications of the invention involving the use of sulfur analogues of the aliphatic monohydric alcohols, i. e., mercaptans, the formation of di-thioesters can sometimes be effected in a manner substantially similar to that described above. Alternatively, in instances where individual mercaptans react directly with aliphatic dibasic acids with difliculty, it is sometimes advantageous first to form a mixture of acid anhydrides from the oxidized acids mixture and then to react the anhydride mixture with the mercaptan. A method of this kind is described in U. S. Patent No. 2,550,141. On the other hand, if anhydride formation is difiicult it may be preferred to form the acyl halides of the complex dibasic acid mixture by reaction of the latter with phosphorus trichloride, phosphorus pentachloride or thionyl chloride, and then to react the mixed acyl halides with the desired marcaptan. The formation of acyl halides and the reaction thereof with alcohols or mercaptans are conventional reactions, forming no part of this invention, and for this reason need not be described in detail.

Alcohols that form suitable esters with the complex oxidized acid mixtures disclosed herein are monohydric alcohols containing 4 to 25 carbon atoms per molecule. Normally liquid alcohols, preferably those containing 5 to 16 carbon atoms per molecule, form especially suitable ester mixtures for the purposes of this invention. Particularly outstanding ester mixtures have been obtained with 0x0 alcohols which comprise mixtures of isomeric, mostly branched chain, primary monohydric alcohols produced by the Oxo synthesis process. The OX0 synthesis process, as is wel1-known involves the catalytic hydroformylation of mono-olefins, such as, for example, hexene, heptene, or octene, usually in the form of a mixture of isomers such as can be obtained by nonselective polymerization of the C C or mixed C and C mono-olefins present in refinery gases, with a mixture of carbon monoxide and hydrogen, to obtain a mixture of oxygenated products, principally aldehydes, having one more carbon atom per molecule than the original mono-olefin followed by catalystic hydrogenation of the aldehydic reaction product thus obtained. Alcohols obtained in this fashion are customarily designated Oxo alcohols. Specific examples of 0x0 alcohols that have been found to form highly effective lubricant mixtures with the acid mixtures disclosed herein include oxoamyl alcohols and oxo-octyl alcohols. The oxo-amyl alcohols were produced by subjecting mixed, isomeric C mono-olefins present in refinery gases to the x0 synthesis process and consisted essentially of isomeric amyl alcohols, the major proportion of which comprised isomeric methyl butanols. The oxo-octyl alcohols referred to were prepared by subjecting a mixture of hepteue isomers, obtained from the fractionation of a copolymer of mixed C and C mono-olefins present in refinery gases, to the Oxo synthesis process. These oxo-octyl alcohols consist mostly of dimethyl hexanols. Examples of other monohydric alcohols, the use of which is included by this invention, are 2-ethyl-hexanol, n-decyl alcohol, oxo-tridecyl alcohol, myristyl alcohol, stearyl alcohol and oleyl alcohol.

While alcohols as such are the normally preferred esterification reactants, equivalent esterification agents such as esters or olefins can be used. For example, instead of octyl alcohol there can be used octene-l, octyl acetate, or octyl formate.

Mercaptans suitable for use in preparing thioester mixtures within the scope of this invention include the thinanalogues or mercaptans corresponding to the above disclosed alcohols. Specific examples of suitable aliphatic monosulfhydric mercaptans are butyl mercaptan, amyl mercaptan, and octyl mercaptan.

The complex, oxidized, carboxylic acid mixtures that are capable of forming synthetic ester mixtures within the scope of this invention are those obtained by nitric acid oxidation of long chain aliphatic hydrocarbons. By way of illustration, satisfactory oxidized acid mixtures can be obtained by partial oxidation of a suitable long chain aliphatic hydrocarbon material, for example, paratlin wax, with an excess, for example, about 2.5 times and up to 60 times, or more, the weight of the wax of nitric acid of at least 50 percent and preferably of at least 70 percent strength, at atmospheric or elevated pressure. i. e., say about to about 2000 p. s. i. a., for example 500 p. s. i. a., at a temperature of about 50 to about 150 C. for example 70 C., for about one-half to about 45 hours, for example hours. The nitric acid oxidation can be stopped at any desired stage. If the reaction is stopped before the oxidation of all of the hydrocarbon material has progressed to the desired degree, two phases will exist in the reaction mixture, an oily phase and an aqueous nitric acid phase. The desired oxidized acids mixture, i. e., that containing dibasic acids, will be found in the aqueous phase of the reaction mixture. When all of the hydrocarbon material has been partly oxidized to the desired degree, the oily phase will have completely disappeared. The total oxidized acids mixture can be used directly in the esterification reaction, after distillation of the aqueous phase reaction product to drive off water and unused nitric acid. The total oxidized acids mixture will contain predominantly aliphatic dibasic acids having 3 to 16 carbon atoms per molecule.

Although suitable oxidized acid mixtures can be obtained by oxidation of the long chain saturated aliphatic hydrocarbons with nitric acid as the only oxidant, as described in the preceding paragraph, we prefer to use, and the invention specifically includes the use of oxidized acid mixtures obtained by oxidation of long chain saturated aliphatic hydrocarbons with nitric acid in conjunction with a free oxygen-containing oxidant such as arr or pure oxygen. The oxygen-containing gas can be used before and/or together with the nitric acid, and when so used it serves to reduce the consumption of nitric acid in the oxidation reaction. An example of a procedure for producing a mixture of dibasic acids by nitric acid oxidation of hydrocarbon material, wherein a free oxygen-containing gas is used as an auxiliary oxidizing agent, is found in copending application Serial 7 No. 376,616, filed August 26, 1953, in the names of Brown, Crowley and Franke, now U. S. Patent No. 2,771,482. Briefly, that patent discloses partial preoxidation of long chain saturated aliphatic hydrocarbons, for example paraifin wax, in a first stage, by passage of a free oxygen-containing gas, e. g., air, through molten paraffin wax at a temperature of about 100 to about 400 C., for example 160 C., in an amount sufficient to provide a free-oxygen-hydrocarbon ratio in the range of about 0.5-2.0: 1, preferably until the air-oxidized product has a saponification number above about 100, usually about 100 to about 450, for example about 230. The air-oxidized product is then further oxidized in a second stage using aqueous nitric acid of at least 50 percent strength, for example 70 percent nitric acid, as an oxidant. The air-oxidized product is reacted with about 2.5 to 20 times, for example 5 times, its weight of nitric acid at a pressure of atmospheric to 1000 p. s. i. a., for example autogenous reaction pressure, at a temperature of about 50 C. to 150 C., for example 90 C., for a period of 1 to 30 hours, for example 20 hours. The nitric acid is removed from the aqueous nitric acid phase material in the reaction product by distillation at reduced pressure to produce a distillation residue mixture, the total oxidized acids mixture containing predominantly aliphatic dibasic acids.

In a preferred embodiment of the above-described nitric acid oxidation process, nitrogen oxides resulting from the nitric acid oxidation of air-preoxidized hydrocarbons are regenerated by reoxidation with a free-oxygen-containing gas, such as air or oxygen, and the regenerated nitrogen oxides are then reused in the oxidation of partly oxidized hydrocarbons. By regenerating at least a portion of the nitrogen oxides produced during the oxidation of the preoxidized hydrocarbons to higher oxides of nitrogen, overall nitric acid consumption is reduced. The nitrogen oxides can be reoxidized apart from the nitric acid oxidation reaction vessel and recycled thereto, or both reactions can be conducted concurrently in the same vessel.

Although it is not necessary for the purposes of this invention, the oxidized acids obtained as described above can be further separated into separate fractions which themselves contain sub-mixtures of oxidized acids that can be esterified to form ester mixtures included by this invention. For example, such an oxidized acids sub-mixture can be obtained from the total oxidized acids mixture that is recovered from the aqueous nitric acid phase of the reaction mixture, after removal of unused nitric acid and water, by solvent extraction of the distilled residue of the total oxidized acids mixture with an inert, essentially water-immiscible solvent that will preferentially dissolve the liquid components of the acid mixture. Preferred solvents are those having a boiling point not greater than about 200 C. Suitable solvents include aromatic hydrocarbons, ketones, ethers, chlorinated hydrocarbons, and nitroparaflins boiling below about 200 C. Specific examples of suitable solvents are benzene, toluene, methyl ethyl ketone, diisopropyl ether, trichloroethylene and nitropropane. After addition of solvent to the distilled residue of oxidized acids, the mixture is chilled and filtered, and the filter cake is washed with additional solvent. The filter cake, referred to herein as precipitated or crystallized acids, comprises a mixture of dibasic acids, the predominant components of which are even-numbered dibasic acids. For example, where parafiin wax or the like is the material subjected to nitric acid oxidation, the precipitated acids, or crystallized acids, will comprise predominantly a mixture of even-numbered dibasic acids containing 4 to 10 carbon atoms. In a specific instance involving the direct nitric acid oxidation of 132 F. melting point parafiin wax with an excess of to percent nitric acid for 30 hours at 75 C. at atmospheric pressure, a total dibasic acids yield of approximately 65 percent, based on the weight of the parafiin wax charge, was recovered. The approximate composition of the precipitated acids fraction obtained from these total oxidized acids, as determined by distillation of the ethyl esters, was as follows:

(yields on basis of paraflin wax charge) Percent Succinic (C 7.8 Adipic (C 6.3 Suberic (C 4.7 Suberic and other 4.4

Another portion of the total, aqueous-phase, oxidized acids mixture that is capable of forming suitable esters within the scope of this invention can be obtained from the filtrate remaining after recovery of the precipitated acids. To obtain this fraction, 21 solution of the filtrate acids, in a solvent of the class indicated, preferably other than benzene, for example, diisopropyl ether, is then ex tracted, preferably several times, for example 3 times, with water. The use of benzene as a solvent at this stage, even when benzene was used as a solvent in the previous extraction, can be avoided by evaporation of the benzene and taking up the residue in a difierent solvent of the class indicated.

After distillation of the extract to drive off water, a mixture of oxidized acids, referred to herein as extracted acids, comprising predominantly aliphatic dibasic acids containing odd numbers of carbon atoms will be obtained. For example, where paraflin wax or the like is the material subjected to nitric acid oxidation, the extracted acids will normally comprise predominantly C aliphatic dibasic acids. In the specific instances described above in connection with the discussion of precipitated acids, the extracted acids recovered from the filtrate remaining after the recovery of the precipitated acids had the following approximate composition as determined by distillation of the ethyl esters: (yields on basis of paraflin wax charge) Percent Malonic (C 2.1 Glutaric (C 4.2 Adipic (C 5.2 Pimelic (C 5.2 Pimelic and other 12.3

Still another oxidized acids fraction capable of forming suitable ester mixtures within the scope of this invention can be obtained from the total oxidized acids mixture resulting from nitric acid oxidation of long chain aliphatic hydrocarbons. More particularly, this fraction, referred to herein as rafi'inate acids, is that remaining in the solvent solution after extraction of the latter with water to remove the extracted acids. The raffinate acids can be used directly to prepare ester mixtures within the scope of this invention after removal of the solvent. The rafiinate acids comprise a mixture of dibasic acids containing a broad spectrum of the dibasic acids present in the total oxidized acids mixture, the dibasic acid content of which is believed to be composed chiefly of dibasic acids containing 4 to 12 carbon atoms. Other materials of unidentified nature, including nitrogen-containing compounds, are also present in the raffinate acid fraction.

The invention is not limited to acids formed from nitric acid oxidation of refined paraffin wax but also includes acid mixtures obtained by nitric acid oxidation of other components of Wax-bearing petroleum fractions, as well as other long chain saturated aliphatic hydrocarbon materials. By long chain is meant a chain of at least 8 carbon atoms. Examples of other long chain saturated aliphatic hydrocarbon materials which can be oxidized with nitric acid to obtain acid mixtures suitable for the purposes of this invention include various petroleum waxes as well as other long chain hydrocarbon components of wax-bearing petroleum fractions, such as paraffin wax distillate, slack wax, crude scale wax, foots oil, cylinder stock, petroleum, microcrystalline wax or the like. Microcrystalline wax differs from paraffin wax primarily in that the former consists mostly of parafiinic hydrocarbons containing about 40 to 50 carbon atoms per molecule, whereas parafin wax consists mostly of long chain parafiinic hydrocarbons within about the C2040 range. Cetane is an example of a pure long chain aliphatic hydrocarbon material which can be subjected to nitric acid oxidation to form suitable dibasic acid mixtures.

The invention can be further understood by reference to the following specific embodiments.

EXAMPLE I A 300 gram sample of refined paratfin wax having a melting point of 132 F. was preoxidized by air blowing with about 7.5 liters per minute of air for 11.5 hours at a temperature of 320 F. At the end of this period the preoxidized product had a saponification number of 237. Six hundred and forty-one grams of the air-preoxidized product obtained as described was charged to a one liter autoclave which was operated in a continuous manner. Nitric acid of 65 percent strength was charged to the autoclave in a 5:1 weight ratio with the air-preoxidized product. The reactants were fed to the autoclave and With drawn continuously at a rate which gave a 30 minute residence time. The vessel and contents were maintained at C. and gaseous oxygen was added and withdrawn continuously at a pressure of 500 p. s. i. g. The autoclave was opened and the aqueous nitric acid phase was distilled to remove unreacted nitric acid. The total oxidized wax acids product had a saponification number of 742.

A 222.2 gram sample of total oxidized wax acids obtained as described was then mixed with 500 grams of p-xlyene and 2.2 grams of p-toluene sulfonic acid and 1146 grams (approximately a 3:1 equivalent weight ratio) of oxo-octyl alcohols consisting predominantly of isomeric dimethyl hexanols and having a boiling range of C. at 760 mm. Hg. The reaction mixture was heated under reflux, with water being trapped off, for about 6 to 7 hours at an average pot temperature of about 168 C. During this period 46 grams of water were trapped off. The reaction product was washed with two percent sodium hydroxide solution and then with water to remove the p-toluene sulfonic acid catalyst and any unreacted oxidized wax acids. The washed product was then stripped of excess alcohol and p-xylene by heating the mixture to a pot temperature of 250 C. at atmospheric pressure. The product was then distilled under vacuum to a maximum temperature of about 94 C. at 5 mm. Hg. pressure. The remaining product consisted essentially of the substantially neutral, di oxo-octyl esters of the total oxidized wax acids fraction. The ester mixture thus obtained had the following properties:

Viscosity, cs.:

65 2567 Viscosity index 148 Pour point, F 75 Flash point, ASTM-D-92 375 Fire point, ASTM-D-92 420 Neutralization number, ASTMD974 1.46

EXAMPLE II At the completion of this period of time a homogeneous.

,3 &

solution was obtained, the absence of an oil phase indicating substantially complete oxidation of hydrocarbon materials to aqueous nitric acid-soluble derivatives. The thus obtained total oxidized acids were distilled to remove excess nitric acid. One hundred and thirty-two grams of distilled residue were obtained. This product was separated into 3 fractions comprising precipitated acids, extracted acids and raifinate acids. Specifically, an excess of benzene was added to the distilled residue and the mixture was chilled and filtered, the filter cake, comprising the precipitated acids, being washed with benzene. Benzene was then evaporated from the filtrate and the remaining liquid was taken up in dicthyl ether. The ether solution was extracted with water three times, following which water was evaporated from the extract to produce the extracted acids fraction. The ether ratiinate was then heated to drive off the solvent and produce a raflinate acid fraction. Thirty-four grams of the filter cake or precipitated acids fraction, 31.9 grams of extracted acids, and 55.2 grams of raifinate acids were obtained.

The extracted acids fraction obtained from the foregoing run was mixed with the extracted acids fractions obtained from three other substantially identical runs to produce approximately 100 grams of extracted acids. Thirty grams of the composite extracted acids were admixed with 0.2 gram p-toluene sulfonic acid and 55 grams of oxo-amyl alcohols. consisting chiefly of isomeric methyl butanols, and the mixture was heated to about l20-l40 C. for about 5 /2 hours under reflux, with water being trapped off. When no further water could be trapped off, the reaction mixture was washed with 5 percent aqueous sodium bicarbonate solution and again with water to remove esterification catalysts and any unreacted oxidized acids. Unreacted oxo-amyl alcohols were removed by distillation and 49.8 grams of the substantially neutral di oxo-amyl esters of extracted oxidized wax acids were obtained. This product was then redistilled to obtain a cut boiling at l342l2 C. at 1 mm. Hg pressure (79 percent of crude product).

The synthetic mixture thus obtained had the following properties:

Viscosity, cs.

In addition the product was found to be crystal clear and freely pourable after storage at -65 F. for 72 hours.

From a comparison of the properties of the foregoing synthetic ester mixtures with the corresponding requirements for certain specific military lubricants, presented for convenience in the table below, it will be seen that the unblended and uncompounded products of this invention meet or almost meet the requirements of these specifications.

It is of course understood that the uncompounded synthetic ester mixtures of this invention can be further improved by blending with various proportions of one or more other synthetic lubricants, or with petroleum lubricants, or with various lubricant improvement agents that are designed to improve one or more characteristics of uncompounded lubricant oils.

The synthetic ester mixtures prepared in accordance with the foregoing examples, and which constitute preferred embodiments of the invention, possess unusually good low temperature characteristics. The low temperature characteristics of the synthetic ester mixtures are shown by reference to the data in the following table:

The results set forth in the foregoing table show that the synthetic ester mixtures prepared in accordance with the examples possess low temperature viscosities below those obtained by extrapolation of the 2l0'i00 F. ASTM temperature viscosity curve. That such properties are not typical of comparable pure dialkyl esters of dibasic acids can be demonstrated by reference to the following table:

Table B Viscosity, cs.

Synthetic esters At 40 F.,

At 210 F., At 100 F.,

actual actual Extrap- Actual olatcd Di-Cg oxo adipato 2. 79 9. 800 1, 037 Di-Cn oxo adiuate 3. 45 12. 8 1,150 1, 955 Dl-Cw oxo adipatc 3. 60 14.43 1, 800 2,954

Data from British Patent, No. 722,534.

The data presented in Table B show that the indicated pure dialkyl esters exhibit greater viscosities at -40 F. than those obtained by extrapolation of the 210-l00 F. ASTM temperature viscosity curves.

Specific examples of other synthetic ester mixtures that have been prepared according to this invention and that have been found to have suitable characteristics either as such or when used as lubricant bases are: the substantially neutral oxo-octyl ester of the extracted acids fraction of the total oxidized acids obtained by nitric acid oxidation of paraffin wax, the substantially neutral oxooctyl ester of the precipitated acids fraction obtained from the total oxidized acids resuiting from nitric acid oxidation of paraffin wax, the substantially neutral oxoamyl and oxo-tridecyl esters of total oxidized acids resulting from nitric acid oxidation of paraffin wax, the substantially neutral oxo-octyl ester of total oxidized acids resulting from nitric acid oxidation of fonts oil, and the substantially neutral oxo-octyl esters of the raflinate acids fraction obtained from the total oxidized acids resulting from the nitric acid oxidation of deoiled foots oil. Speific examples of other synthetic ester mixtures included by the invention are the substantially neutral 2-ethylhexyl, myristyl, and stearyl esters of total oxidized acids, the precipitated acids fraction thereof, the extracted acids fraction thereof and the rathnate acids fraction thereof, said total oxidized acids being obtained by the nitric acid oxidation of paraffin wax, cetane, foots oil, and microcrystalline wax. The thin-analogues of the herein disclosed specific synthetic ester mixtures are also included by the invention.

As has been indicated, the synthetic ester compositions of this invention can be used as lubricants either as such or in blends with petroleum oils or other synthetic lubricants including pure dibasic acid esters, long chain monoesters, glycol diesters, tribasic acid esters and esters of polyhydric alcohols. When used as lubricants either alone or in admixture with other materials having lubricating properties, the synthetic ester mixtures of this invention can have added thereto one or more additional agents designed to improve one or more properties thereof. Thus there can be added to the synthetic esters and lubricant blends containing the same viscosity index improvers, pour point improvers, oxidation inhibitors, corrosion inhibitors, detergents, dispersants, bearing corrosion inhibitors, thickening agents and the like.

The synthetic ester mixtures of this invention find additional utility when admixed with hydrocarbon fuels such as motor gasoline, diesel fuel, furnace oil, marine gasoline, aviation gasoline, jet fuel and the like. When added to such fuels in minute quantities the synthetic ester mixtures disclosed herein function as valve top and upper cylinder lubricants, fuel injector lubricants and fuel pump lubricants.

In addition, the synthetic ester mixtures of this invention have been found to possess valuable rust and corrosion inhibiting characteristics. Thus, for example, when added to gasoline in even the relatively small proportion of 16 pounds per thousand barrels, these synthetic ester mixtures were found to reduce corrosion of a steel test specimen that had been partly immersed in contiguous layers of the gasoline and water. Test results illustrating the improvement obtainable by the use of the synthetic ester mixtures are presented below.

Table C Composition 1 2 3 4 5 Make-up: Percent by vol.:

Base gasoline Added: 1b./l,000 bhl.:

Di-oxo-octyl ester of distn. residue from nitric acid oxidation of airoxidized paraffin Di-o xo-tridecyl ester of distn. residue from nitric acid oxidation of airoxidized deoiled toots oil Distilled di-oxo-octyl ester of dist'n residue from nitric acid oxidation of air-oxidized deoiled ioots oil Distilled di-oxo-octyl ester of rattlnate acids from nitric acid oxidation of air-oxidized deoiled ioots oil..

Inspections:

Rust inhibition, distilled water: extent of rusting of steel specimen:

Exposed to air phase at None.. do-..

None.

None. .do...

. ..do.. Trace D0. Do.

...do... do...

..do... do.-.

7 days Exposed to water phase at time oi- Trace. Light.

Trace Light Light.

Heavy Trace Light Trace Light Numerous modifications of the herein disclosed specific embodiments can be resorted to without departure from the spirit or scope of the invention. Accordingly, only such limitations should be applied to the invention as appear in the appended claims.

We claim:

1. A composition of matter selected from the group consisting of substantially neutral alkyl esters and alkyl None. Do.

thioesters of a mixture of dicarboxylic acids obtained by partial oxidation of a long chain saturated aliphatic hydrocarbon material with an excess of nitric acid of at least 50 percent strength, at a temperature of about 50 to about 150 C., for about one-half to about 45 hours, where said alkyl substituents contain 4 to 25 carbon atoms.

2. A composition of matter comprising substantially neutral esters of (a) an aliphatic monohydric alcohol containing 5 to 16 carbon atoms per molecule, and (b) a mixture of dicarboxylic acids obtained by partial oxidation of a preoxidized long chain hydrocarbon component of a wax-bearing petroleum fraction with about 2.5 to about 20 times its weight of nitric acid of at least 50 percent strength, at a pressure of about 15 to about 2000 p. s. i. a., at a temperature of about 50 to about 150 C., for about one-half to about 45 hours, the preoxidation being effected by contacting said hydrocarbon component with a gas that contains free oxygen at a temperature of about to about 400 C., in an amount sufiicient to furnish an oxygenzhydrocarbon ratio in the range of about 0.5 to 2011, until the preoxidized material has a saponification number of above about 100.

3. The composition of claim 2 where the mixture of dibasic acids is the residue resulting from distillation of water and nitric acid from the product of said partial oxidation with nitric acid.

4. The composition of claim 2 where the mixture of dibasic acids is a mixture of precipitated acids remaining after separation of the liquid components of the residue resulting from distillation of water and nitric acid from the product of said partial oxidation with nitric acid.

5. The composition of claim 2 where the mixture of dibasic acids is a mixture of preferentially water-soluble acids extracted from the liquid components of the residue resulting from distillation of water and nitric acid from the product of said partial oxidation with nitric acid.

6. The composition of claim 2 where the mixture of dibasic acids is a mixture of acids remaining after separation of the preferentially water-soluble acids from the liquid components of the residue resulting from distillation of water and nitric acid from the product of said partial oxidation with nitric acid.

7. A composition of matter comprising substantially neutral esters of (a) branched chain Oxo alcohols containing 5 to 16 carbon atoms, and (b) a mixture of dicarboxyiic acids obtained by partial oxidation of an airpreoxidized long chain hydrocarbon component of a waxbearing petroleum fraction with about 2.5 to about 20 times its weight of nitric acid of at least 50 percent strength, at a pressure of about 15 to about 2000 p. s. i. a., at a temperature of about 50 to about C., for about one-half to about 45 hours, where the air-preoxidation is effected by contacting the hydrocarbon component with air at a temperature of about 100 to about 400 C., in an amount sufficient to provide an oxygenzhydrocarbon component ratio in the range of about 0.5 to 2.011, until the preoxidized material has a saponification number of above about 100.

8. The product of claim 7 where the mixture of dicarboxylic acids is the distillation residue resulting from the distillation of water and nitric acid from the product obtained by partial oxidation of an air-preoxidized long chain hydrocarbon component of a wax-bearing petroleum fraction with about 2.5 to about 20 times its weight of nitric acid of at least 50 percent strength, at a pressure of about 15 to about 2000 p. s. i. a., at a temperature of about 50 to about 150 C., for about one-half to about 45 hours, where the air-preoxidation is effected by contacting the hydrocarbon component fraction with air at a temperature of about 100 to about 400' C., in an amount sufiicient to provide an oxygemhydrocarbon component ratio in the range of about 0.5 to 2.021, until the preoxidized material has a saponification number of above about 100.

9. The product of claim 7 where the mixture of di' curboxylic acids is a mixture of preferentially water-soluble acids extracted with water from a solution of mixed acids in an inert, water-immiscible solvent, said mixed acids having been obtained by dissolving, with an inert, water-immiscible solvent, the liquid portion of the total mixture of dicarboxylic acids obtained by partial oxidation of an air-preoxidized long chain hydrocarbon component of a wax-bearing petroleum fraction with about 2.5 to about 20 times its weight of nitric acid of at least 50 percent strength, at a pressure of about 15 to about 2000 p. s. i. a., at a temperature of about 50 to about 150" C., for about one-half to about 45 hours, where the air-preoxidation is effected by contacting the hydrocarbon component with air at a temperature of about 100 to about 400 C., in an amount sufiicient to provide an oxygenzhydrocarbon component ratio in the range of about 0.5 to :1, until the preoxidized material has a saponification number of above about 100.

10. A composition of matter comprising substantially neutral esters of branched chain oxo-octyl alcohols and a mixture of dicarboxylic acids obtained by partial oxida tion of an air-preoxidized paraffin wax fraction with about 2.5 to about 20 times its weight of nitric acid of at least 50 percent strength, at a pressure of about 15 to about 2000 p. s. i. a., at a temperature of about 75 to about 130 C., for about one-half to about 45 hours, where the air-preoxidation is effected by contacting the paraffin wax with air at a temperature of about 150 to about 190 C., in an amount sufficient to provide an oxygen: parafiin wax ratio in the range of about 0.5 to 2.0:1, until the preoxidized material has a saponification number of above about 100.

11. A composition of matter comprising substantially neutral esters of branched chain oxo-amyl alcohols and a mixture of preferentially water-soluble dicarboxylic acids extracted with water from a solution of mixed acids in an inert, water-immiscible solvent therefor, said mixed acids having been obtained by dissolving, with an inert, water-immiscible solvent, the liquid components of the total mixture of dicarboxylic acids obtained by partial oxidation of an air-preoxidized paraflin wax with about 2.5 to about 20 times its weight of nitric acid of at least 50 percent strength, at a pressure of about 15 to about 2000 p. s. i. a., at a temperature of about 75 to about 130 C., for about one-half to about 45 hours, where the airpreoxidation is eflected by contacting the paraffin wax with air at a temperature of about 150 to about 190 C., in an amount sutficient to provide an oxygen; paraffin wax ratio in the range of about 0.5 to 20:1, until the preoxidized material has a saponification number of above about 100.

12. A process comprising effecting esterification of at least an equivalent amount of an aliphatic monohydric alcohol containing 4 to carbon atoms per molecule and a mixture of dicarboxylic acids obtained by partial oxidation of a long chain saturated aliphatic hydrocarbon material with an excess of nitric acid of at least 50 percent strength, at a temperature of about 50 to about 150 C. for about one-half to about 45 hours.

13. A process comprising preoxidizing a long chain bydrocarbon component of a wax-bearing petroleum fraction at a temperature of about 100" to about 400 C. with a gas that contains free oxygen in an amount sutficient to provide an oxygenzhydrocarbon component ratio in the range of about 0.5 to 2.0: 1, until the preoxidized material has a saponification number of above about 100, further oxidizing the preoxidized material by contact thereof with about 2.5 to about 20 times its weight of nitric acid of at 12 least 50 percent strength, at a temperature of about 50 to about 150 C., at a pressure of about 15 to about 2000 p. s. i. a., for about one-half to 45 hours, and reoxidizing nitrogen oxides liberated during said oxidizing with nitric acid by contact with free oxygen and recovering an aqueous phase containing a mixture of dicarboxylic acids, removing unused nitric acid and water from said aqueous phase, and esterifying at least a portion of the remaining mixture of dicarboxylic acids with at least an equivalent amount of Oxo alcohols containing 5 to 16 carbon atoms.

14. The process of claim 13 where the mixture of dicarboxylic acids is the residue resulting from distillation of water and nitric acid from the product of said partial oxidation with nitric acid.

15. The process of claim 13 where the mixture of dicarboxylic acids is the mixture of precipitated acids remaining after separation of the liquid components of the residue resulting from distillation of water and nitric acid from the product of said partial oxidation with nitric acid.

16. The process of claim 13 where the mixture of dicarboxylic acids is a mixture of preferentially watersoluble acids extracted from the liquid components of the residue resulting from distillation of water and nitric acid from the product of said partial oxidation with nitric acid.

17. The process of claim 13 where the mixture of dicarboxylic acids is a mixture of acids remaining after separation of the preferentially water-soluble acids from the liquid components of the residue resulting from distillation of water and nitric acid from the product of said partial oxidation with nitric acid.

18. A process comprising preoxidizing paratiin wax with air at a temperature of about 150 to about 190 C., in an amount sufficient to provide an oxygenzparafiin wax ratio in the range of about 0.5 to 2.0:], until the airoxidized product has a saponification number of above about 100, further oxidizing the preoxidized material by contact thereof with about 2.5 to about 20 times its weight of nitric acid of at least 50 percent strength, at a temperature of about to about C. and at a pressure of about 15 to about 1000 p. s. i. a., recovering an aqueous phase containing a mixture of dicarboxylic acids, removing unused nitric acid and water from said aqueous phase, and esterifying the total remaining mixture of dicarboxylic acids with at least an equivalent amount of oxo-octyl alcohols.

19. A process comprising preoxidizing paraffin wax with air at a temperature of about to about C., in an amount sutficient to provide an oxygen: paraffin wax ratio in the range of about 0.5 to 2.0:1, until the airoxidized product has a saponification number of above about 100, further oxidizing the preoxidized material by contact thereof with about 2.5 to about 20 times its weight of nitric acid of at least 50 percent strength, at a temperature of about 75 to about 130 C. and at a pressure of about 15 to about 2000 p. s. i. a., recovering an aqueous phase containing a mixture of dicarboxylic acids, removing unused nitric acid and water from said aqueous phase, dissolving the liquid components of the remaining mixture of dicarboxylic acids with an inert, water-immiscible solvent, and solvent extracting the thus-formed solution with water to obtain a mixture of extracted, preferentially water-soluble dicarboxylic acids, esterifying the extracted acids with at least an equivalent proportion of oxo-amyl alcohols.

References Cited in the file of this patent UNITED STATES PATENTS 2,729,665 Buckmann Jan. 3, 1956 

1. A COMPOSITION OF MATTER SELECTED FROM THE GROUP CONSISTING OF SUBSTANTIALLY NEUTRAL ALKYL ESTERS AND ALKYL THIOESTERS OF A MIXTURE OF DICARBOXYLIC ACIDS OBTAINED BY PARTIAL OXIDATION OF A LONG CHAIN SATURATED ALIPHATIC HYDROCARBON MATERIAL WITH AN EXCESS OF NITRIC ACID OF AT LEAST 50 PERCENT STRENGHT. AT A TEMPERATURE OF ABOUT 50* TO ABOUT 150*C., FOR ABOUT ONE-HALF TO ABOUT 45 HOURS, WHERE SAID ALKYL SUBSTITUENTS CONTAIN 4 TO 2K CARBON ATOMS. 